A reactor of this general type is disclosed in European Patent Specification No. 0 208 139A1. In such document, there is described a reactor comprising a housing within which is defined a chamber. The chamber is connected to a source of reduced or excess pressure depending upon whether the material is to be degassed or gassed. Within the chamber, a plurality of rotatably drivable, axis-parallel, intermeshing conveying shafts are mounted. The shafts are disposed around the interior periphery of the housing and each shaft meshes with the two shafts adjacent thereto. The shafts are all rotated in the same direction so that thin layers of the material to be treated are formed on the portions of the shafts which face into the chamber. Effectively, therefore the degassing or gassing chamber is formed radially inwardly of the conveying shafts. The shafts are not free to move axially but the longitudinal ends thereof are guided upwardly into a transmission unit so that they can be rotated. Such thin-layer reactor carries out an operation for degassing or gassing the material. Primarily, this prior specification is concerned with providing a system for sealing the conveying shafts. To effect gassing or degassing, the chamber, which is sealed at its upper and lower ends, is subjected either to an excess pressure or to reduced pressure, which latter may be a vacuum.
The particular advantage of such an arrangement is that very thin layers of molten material are formed on the circumferential portions of the conveying shafts which face into the central degassing chamber. The chamber will, henceforth, be referred to as a degassing chamber although it will be readily apparent from the foregoing that it can equally act as a gassing chamber. The thickness of the layers of molten mass is dependent upon the spacing between the individual, intermeshing conveying shafts. The material to be treated which, in this instance, is in the form of a molten mass and is to be degassed, is fed into the reactor such that it passes onto the external surface of the intermeshing conveying shafts. Due to their rotation and to their surface geometry, the conveying shafts carry the molten mass into the central degassing chamber. In such chamber, the volatile components entrapped in the thin layers of molten mass are diffused onto the surface of the molten mass as a result of the reduced pressure being formed, and they are removed by suction.
Due to the formation of these thin layers of molten mass, thin-layer reactors are particularly suitable for removing volatile components with the exception of a few parts per million thereof, from a molten mass or from a fluid. In particular, however, the parallel disposition of the intermeshing shafts ensures that all of the molten mass is spread to form thin layers and, in consequence, the volatile components can be removed therefrom in a highly satisfactory manner.
However, in such thin-layer reactors, it has proved particularly difficult to seal the individual, intermeshing, conveyor shafts from the drive mechanism. This is essential if the pressure in the central degassing chamber is to remain as low as 10.sup.-4 bar.
Complex sealing systems are required for this purpose and one such system is described in detail in the above-numbered European Patent Specification. Moreover, a complex transmission unit is required to rotate the intermeshing conveying shafts accurately and in the same direction. Such a transmission unit is disclosed in German Patent Specification No. 30 30 541.
Furthermore, in a thin-layer reactor of the above-described type, it is necessary to rotate the housing surrounding the conveying shafts in an oscillatory manner. This is to prevent layers of the material being processed from fritting or caking together on the internal wall of the housing. A system designed to achieve such oscillation is disclosed in German Patent Specification No. 35 13 536.